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A number of Chinese netizens report that since May 6 2011 visiting overseas website via China Telecom and China Unicom has become highly unstable. This time the disruption mainly affected corporate connections, including university, while ADSL connection at home performs normally.

Some technology bloggers point out that the Great Fire Wall is now able to monitor data flow of local IP and impose restriction when it detect large amount of access to certain overseas IP addresses. Some are worried that the mechanism may result in a de facto white listing of overseas websites.

Corporate and university connection affected

Prominent Technology blogger William Long points out that the blocking this time is targeted at corporate user in order to stop people from visiting overseas website via corporate network and connection.

He runs a test in his office at Shenzhen and found out that he cannot connect to certain overseas IP addresses (119.145.47.102). Below shows the detail of the test results:

The Southern Medical University also has suffered from the disruption and explained the situation that China Telecom has restricted the IP access of the university to overseas websites. Zhejiang University also has similar problem [zh], the school VPN's overseas connection has been disrupted. (via William Long)

Many Internet companies suffer from connection problem in Mainland, including Baidu, Tencent, Alibaba and their subsidiary companies. Restriction has been imposed for accessing overseas websites including Apple Company's app store. Some analysts said that the GFW is now able to detect encrypted data flow and block a specific IP addresses. Many Internet Companies’ ports are under restriction.

VPN and circumvention tools forbiddened

In order to tackle with the problem, the IT department of certain corporate has issued the following notices: (via Twitter user @yegle)

Re-posting the notice: Dear colleague, when using the corporate network, do use circumvention tools and VPN to get access to overseas websites. Such act would result in the blocking of corporate port to overseas IPs (For example, access to Google and MSN has become highly unstable). It will also bring trouble to the company and individuals. Please be careful and try to avoid this in your daily work.

A notice from the Chinese Academy of Sciences has confirmed netizens’ speculation:

CAS IHEP: Our faculty's access to overseas websites have been disrupted in the past few days. Upon investigation, the reason is because some users have used circumvention tools to get access to illegal content, hence the public security bureau has black-listed our faculty's IP. Here I remind everyone to follow the rule when using Internet, don't use illegal means to get access to illegal information!